Just had this problem on my 2011 XF and thanks to you guys it saved the mechanic a lot of time and bother. He said that the problem had been caused by a magnet that had come away from its fixing on a chipboard on the fuel pump that he accessed from under the back seats. He put the magnet back, gave the chipboard a clean, crimped all of the wires for good measure and charged me £60 for labour only. To top it off, I've got more fuel left than I thought I did. Wahaay!